Importance of attributable risk in monitoring adverse events after immunization:: Hepatitis B vaccination in children

Objectives. Most vaccine safety data present only the postvaccination incidence of all adverse events rather than an estimate of attributable risk. This study sought to illustrate the difference between the 2 estimates with data from a hepatitis B immunization program. Methods. The incidence of health problems occurring before and after each dose of hepatitis B vaccine in a cohort of 1130 children were compared. Results. Although 47.5% of all children reported an adverse event during the following each of the 3 doses, attributable to immunization occurred in only 10.6% of children. Conclusions. Postimmunization incidence systematically overestimates the risk of adverse events. Estimating actual attributable risk is necessary to avoid false beliefs regarding immunization.